Hydraulic motor drive

ABSTRACT

A hydraulic drive device having a hydraulic motor section fixedly connected to a gear reduction section. The hydraulic motor section includes movable pistons disposed within a rotatable cylinder barrel and maintained in engagement with an inclined swash or cam plate for causing rotation of the cylinder barrel. The cylinder barrel is rotatably connected to and drives a shaft, which shaft has a gear thereon disposed in meshing engagement with a further enlarged gear disposed within the gear reduction section. Suitable passages and grooves are provided in the cylinder barrel to permit leakage fluid within the pump section to be discharged into the reduction gear section. One-way check valve devices coact between the motor ports and the gear reduction section for enabling discharge of leakage fluid into the low pressure or discharge port.

I Umted States Patent [191 [111 3,744,377 Lauck July 10, 1973 HYDRAULICMOTOR DRIVE [57] ABSTRACT Inventor! J Lallck, Colfax Avenue, A hydraulicdrive device having a hydraulic motor sec- Benton Harbor, Mlch- 49022tion fixedly connected to a gear reduction section. The h draulic motorsection includes movable istons dis- I 7 y P [22] Filed Apr 12 19 lposed within a rotatable cylinder barrel and maintained PP N01 ,358 inengagement with an inclined swash or cam plate for causin rotation ofthe cylinder barrel. The cylinder b l bl d d d h f 91 89 1 499, 92 86 weY mes a S a g M i /F04b 4 which shaft has a gear thereon disposed inmeshing en- [58] Field oisQQiEiQIIIIIIIIIIIIIIIIIIIBiM, 486, 489,gagemem with a further enlarged gear disPosed Within 91/506 92/86 865the gear reduction section. Suitable passages and grooves are providedin the cylinder barrel to permit [56] References Cited leakagle fluiidwithin the pump secotion to be gisclhargled into t e re uction gearsection. ne-way c ec va ve UNITED STATES PATENTS devices coact betweenthe motor ports and the gear re- 3,006,284 10/1961 Pitt et al. 92/86 Xduction section f enabling discharge f leakage fl id gglglgy Q into thelow pressure or discharge port. 3:514:223 5/1970 Hare 91/499 12 C i 8Drawing Figures 3,237,569 3/1966 Reaume 9l/499 Primary ExaminerManuel A.Antonakas Att0rneyW00dhams, Blanchard and Flynn l2 I7 28 2754- 29 47 IIN V EN TOR.

K/ w v m A 0 1 I AM HYDRAULIC MOTOR DRIVE FIELD OF THE INVENTION Thisinvention relates to a hydraulic drive device which includes a hydraulicmotor section and a gear reduction section and, in particular, to animproved hydraulic drive device having suitable pressure release meansfor preventing excessive pressure build-up within the device duringoperation or during rapid rotation reversals.

BACKGROUND OF THE INVENTION Piston-type hydraulic motors which utilizean inclined cam or swash plate are well known, and numerousmodifications and variations of this type of hydraulic motor have beendeveloped for different use situations. However, hydraulic motors ofthis type have long been plagued with the problem of fluid seepage orleakage into the housing chamber which surrounds the cylinder barrel.Such leakage fluid, if permitted to collect within the housing chamber,will result in a substantial pressure build-up and, since thepressurized leakage fluid is in contact with the pistons, it can exertan undesirable counteracting force on the pistons which tends to retardthe pistons during their power stroke, thus disrupting the efficientoperation of the fluid motor.

Hydraulic motors of the cam or swash plate type have also not performedsuccessfully in use situations wherein the motor is subject to rapidrotation reversals, which rotation reversals result in at least a shortduration pressure build-up in the fluid trapped within the motorhousing. These pressure build-ups or pressure pulses can be extremelydamaging to the motor seals and other related components.

Accordingly, it is an object of the present invention to provide animproved hydraulic drive device which includes a piston-type hydraulicmotor connected to and in communication with a gear box, and wherein thehydraulic drive device includes suitable pressure release means forpreventing the development of excessive fluid pressures within eitherthe motor section or the gear box.

It is another object of the present invention to provide an improvedhydraulic drive device, as aforesaid, which includes suitable one-waycheck valve systems coacting with the motor ports for enabling leakagefluid to be freely discharged to the low pressure or discharge motorport.

A further object of the invention is to provide an improved hydraulicdrive device, as aforesaid, which will permit instant reversing of thehydraulic motor without causing excessive pressures to be developed ineither the motor section or the gear box section.

It is still a further object of the present invention to provide animproved hydraulic drive device, as aforsaid, which includes a desirablevent passageway system within the motor section for preventing excessivequantities of leakage fluid from accummulating within the motor housing.

Still a further object of the present invention is to provide animproved hydraulic drive device, as aforesaid, which is particularlysuitable for use in conveyors or driving vehicles, such as lift trucksand the like, for permitting instant reversing or hydraulic braking ofthe vehicle.

Other objects and purposes of the invention will be apparent to personsacquainted with devices of this type upon reading the followingspecification and inspecting the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of animproved hydraulic drive device constructed according to the presentinvention.

FIG. 2 is a front view, as taken from the right side of FIG. 1, of thehydraulic drive device of the present invention.

FIG. 3 is a fragmentary sectional view taken substantially along theline III-III of FIG. 2.

FIG. 4 illustrates the rear wall of the port plate.

FIG. 5 is an enlarged, fragmentary sectional view taken substantiallyalong the line VV of FIG. 4.

FIG. 6 illustrates the front wall of the cylinder barrel.

FIG. 7 is a fragmentary sectional view of the front end of the cylinderbarrel as taken substantially along the line VII-VII of FIG. 6.

FIG. 8 is an enlarged, fragmentary sectional view of the pressurerelease means.

Certain terminology will be used in the following descriptions forconvenience in reference only and will not be limiting. The wordsupwardly, downwardly, rightwardly and leftwardly will designatedirections in the drawings to which reference is made. The words frontand rear will refer to the right and left sides of the device,respectively, as illustrated in FIG. 1. The words inwardly and outwardlywill refer to directions toward and away from, respectively, thegeometric center of the device and designated parts thereof. Saidterminology will include the words above specifically mentioned,derivatives thereof, and words of similar import.

SUMMARY OF THE INVENTION In general, the objects and purposes of theinvention are met by providing a hydraulic drive device which includes ahydraulic motor section and a gear reduction section fixedly connectedto the motor section. The motor section includes a cylinder barrelhaving a plurality of bores for slideably supporting reciprocatingpistons, which pistons coact with an inclined cam or swash plate forcausing rotation of the cylinder barrel. The cylinder barrel rotates apump shaft which is drivingly connected to the gear reduction section.The motor section includes a pair of ports which permit fluid to besupplied to or discharged from the cylinder bores for causing actuationof the motor section. The motor section includes suitable passages whichprovide communication between the motor chamber and a chamber in thegear reduction section to permit the leakage fluid in the motor sectionto escape into the gear reduction chamber. Pressure release devices,particularly one-way check valves, coact between the ports of the motorsection and the gear reduction chamber for enabling the leakage fluid tobe discharged to the low pressure or discharge port of the motorsection.

DETAILED DESCRIPTION FIG. 1 illustrates therein a hydraulic drive device11 constructed according to the present invention. The

drive device 11 includes a hydraulic motor section 12 Considering firstthe hydraulic motor section 12, same includes a housing 16 defining acylindrical chamber 17 therein. A swash plate cover 18 and a port plate19 are fixedly connected to the housing 16 adjacent the opposite endsthereof. A rotatable pump shaft 21 is concentrically disposed within thechamber 17 and is rotatably supported adjacent the opposite ends thereofby antifriction bearings 22 and 23. A bearing cover 24 is fixedlysecured to the swash plate cover 18 for closing the one end of thehousing.

The pump shaft 21 has a cylinder barrel 26 nonrotatably but axiallyslideably mounted thereon and interconnected by conventional means, suchas a key (not shown). Cylinder barrel 26 has a plurality, such as five,of circumferentially spaced cylinders or bores 27 formed therein in adirection substantially parallel to the longitudinal axis of the pumpshaft 21. A piston 28 is slideably disposed within each of the bores 27and is resiliently urged outwardly of the bore by a compression spring29 disposed between the piston and the bottom wall of the bore. Thesprings 29 resiliently urge the rounded nose or end portions of thepistons 28 into bearing engagement with a rotatable cam or swash plate31. The swash plate 31 is rotatably supported on the inclined inner wall32 of the swash plate cover 18 by a radial roller bearing 33 and athrust roller bearing 34, the latter being disposed in rollingengagement with a hardened thrust washer 36.

The pump shaft 21 extends through the swash plate 31 and has a thrustwasher 37 axially secured thereto, which thrust washer functions as aseat for one end of a compression spring 38. The other end of the spring38 bears against the cylinder barrel 26 and, in conjunction with thepiston springs 29, resiliently urges the cylinder barrel 26 axiallyrelative to the pump shaft 21 so that the axial end wall 39 (FIG. 3) ofthe rotating cylinder barrel 26 is resiliently urged into rotatablesliding and sealing engagement with the inner wall 41 of the port plate19.

The port plate 19 has a pair of radial port openings 42 and 43 (FIG. 4)formed therein, which openings respectively communicate at their innerends with kidney-shaped ports 44 and 46 formed in the inner wall 41. Theports 44 and 46, which function as either fluid supply or dischargeports, are disposed for intermittent communication with furtherkidney-shaped ports 47 (FIG. 6) formed in the axial end wall 39 of thecylinder barrel 26, which ports 47 respectively communicate with thecylinder bores 27.

The cylinder barrel 26 has a small bleed passage 48 extending axiallytherethrough whereby the rearward end of passage 48 communicates withthe motor chamber 17. The forward end of the bleed passage 48communicates with an annular groove 49 (FIG. 7) formed in the axial endwall 39. Groove 49, through intermediate radial passages 51,communicates with art annular clearance space 52 (FIG. 1) providedbetween the pump shaft 21 and the port plate 19.

The cylinder barrel 26 has a further annular groove 53 (FIG. 7) formedon the axial end wall 39, which groove 53 is disposed radially outwardlyof and encircles the kidney-shaped ports 44, 46 and 47. The annulargroove 53 communicates through intermediate radial passages 56 with anannular clearance space 54 (FIG. 1) provided between the housing 16 andthe cylinder barrel 26. The bleed passage 48 and the annular grooves 49and 53 permit leakage fluid within the motor section 17 to be suppliedto the annular clearance space 52, from which the leakage fluid flowsthrough the antifriction bearing 22 into the gear box 13. The manner inwhich this flow occurs will be explained in greater detail hereinafter.

Considering now the gear box 13, same includes a housing 61 whichdefines a chamber 62 therein in communication with the annular clearancespace 52. The housing 61 includes a front cover member 63 fixedlyconnected to an intermediate member 64, which in turn is fixedlyconnected to the front face of the port plate 19. The intermediatemember 64 supports a radial roller bearing 66 which rotatably supportsthe inner end of the output shaft 14. The intermediate member 64 alsocooperates with a suitable shoulder or abutment formed on the shaft 14for confining a conventional thrust roller bearing 67 therebetween. Theforward end of the output shaft 14 extends outwardly of the front cover63 and is disposed in rotatable sealing engagement with a resilientelastomeric O-ring 68 mounted on the front cover 63.

A driven gear 71 is disposed within the gear box chamber 62 and issupported on and nonrotatably connected to the output shaft 14, as bythe integral hub portion 72. A roller bearing 73 coacts between the hubportion 72 and the front cover 63 for rotatably supporting both thedriven gear 71 and the output shaft 14.

The driven gear 71 has internal gear teeth 74 thereon disposed inmeshing engagement with similar external gear teeth formed on a drivegear 76. The drive gear 76 is coaxial with and nonrotatably connected tothe pump shaft 21 so as to be rotatably driven thereby. The drive gear76 is, in the illustrated embodiment, formed integrally on the forwardend of the pump shaft 21. The drive gear 76, as illustrated in FIG. 1,preferably has a diameter which is only a small fraction of the diameterof the internal driven gear 71 to provide a rather large gear ratiotherebetween, whereby the rotational speed of the drive gear 76 isseveral times greater than the rotational speed of the output shaft 14.This arrangement of the gears 76 and 71 results in the output shaft 14being substantially parallel to but laterally offset from the pump shaft21.

The gear box 13 also has associated therewith suitable pressure releasemeans 81 for preventing excessive fluid pressure from developing withinthe gear box chamber 62. The pressure release means 81 specificallycomprises a one-way check valve system (FIG. 8) which includes a checkvalve member 82 slideably disposed within a bore 83 formed in the frontface of the port plate 19. The bore 83 communicates at its rearward endwith the kidney-shaped port 46 and at its forward end with the gear boxchamber 62 by means of an intermediate opening 84 formed in theintermediate member 64. An annular valve seat member 86 is disposed inthe bore 83 adjacent the interface between the port plate 19 and theintermediate member 63 for creating a sealing relationship with thecheck valve member 82, thereby normally preventing flow of fluid throughthe bore 83.

The check valve member 82, as illustrated in FIG.8, has a cuplikeconfiguration and includes a conical end wall 87 which is fixedly, hereintegrally, connected to an annular skirt or sidewall 88 which isslideably disposed within the bore 83. The check valve has a recess 89in the interior thereof disposed for communication with thekidney-shaped port 46, and a plurality of ports or openings 91 extendthrough the conical end wall 87 for providing flow communication betweenthe opposite sides of the check valve 82 when the check valve is moved(upwardly in H0. 8) out of seating engagement with the seat member 86.

A further pressure release means 92 (FIG. 3) provides communicationbetween the gear box chamber 62 and the other kidney-shaped port 44. Thepressure release means 92 is also a one-way check valve system and isidentical to the pressure release means 81. Further description thereofis thus not believed necessary.

OPERATION The operation of the invention will be briefly described indetail hereinbelow for a better understanding thereof.

Assuming that a pressurized fluid is continuously supplied to one of theport openings, such as the port opening 42, then the fluid will flowinto kidney-shaped port 44 and then through the further port 47 into thebores 27 formed in the cylinder barrel 26. The pressure fluid causes thepistons 28 to be urged axially. rearwardly (leftwardly) in FIG. 1) and,due to the coaction between the pistons 28 and the rotatable swash plate31, causes the cylinder barrel 26 and the shaft 21 to be rotated. Due tothe angular orientation of the swash plate 31, the pistons 28 are underpressure during approximately one-half a revolution, during which thepistons are axially extended outwardly from their respective bores.During the other half revolution, the swash plate 31 causes the pistonsto be slideably moved back into their bores causing a discharge of thefluid from the bores 27 into the other kidney-shaped port 46 and thenceout the other port opening 43. The kidneyshaped cylinder ports 47 arethus connected to the inlet pressure fluid during approximately 180 ofrotation, and to the discharge or low pressure side of the system duringapproximately the remaining 180 of rotation. The rotation of the pumpshaft 21 by the cylinder barrel 26 also causes a corresponding rotationof the drive gear 76, which in turn drives the driven gear 71 and theoutput shaft 14. The operation of the hydraulic motor section 12 is thussubstantially conventional and further description thereof is notbelieved necessary. However, it should be noted that, in many usesituations, the pressurized fluid is alternately supplied to the portopenings 42 and 43 to permit reverse rotation of the cylinder barrel,whereby the port openings 42 and 43 thus also alternately act asdischarge ports.

During operation of the hydraulic motor section 12, some fluidinherently leaks or seeps into the motor chamber 17. For example, somefluid leaks between the relatively sliding faces 39 and 41, whichleakage fluid flows into the collection grooves 49 or 53. The fluid inthe collection groove 53 flows throughthe radial passages 56. andthrough the annular clearance space 54 into the motor chamber 17. Otherfluid will also seep or leak between the pistons 28 and the surroundingwalls of the bores 27 into the motor chamber 17. The leakage fluidwithin the motor chamber 17, if permitted to remain, would graduallycollect and cause a substantially high pressure build-up to occur withinthe motor chamber 17, which pressure build-up would reduce or entirelydisrupt the efficient operation of the motor section 12. To prevent anypressure build-up of the leakage fluid within the motor chamber 17, thepresent invention provides the bleed passage 48 which extends axiallythrough the cylinder barrel 26, whereupon the leakage fluid within themotor chamber 17 passes through the bleed passage 48 into the annularcollection groove 49. The leakage fluid then flows through the radialpassages 51 into the annular clearance space 52, and thence through theroller bearing 22 into the gear box chamber 62. The leakage fluid withinthe chamber 62 thus effectively lubricates the gears 71- and 76.

When the pressure of the leakage fluid within the gear box chamber 62increases to a predetermined level, then the fluid in chamber 62 willflow through whichever pressure release means 81 or 92 is associatedwith the low pressure or discharge port, thereby permitting the leakagefluid to be discharged to the low pressure side of the external fluidsystem. For example, when the port openings 43 and kidney-shaped port 46constitutes the discharge port, then the fluid in gear box chamber 62will cause the check valve 82 of the pressure release means 81 to bemoved away from the seat 86, thereby enabling the leakage fluid to flowinto the port 46 and thence out the opening 43. In situations wherepressureized fluid is continuously supplied to the other port 44, thenthe other pressure release means 92 will be continuously maintained inthe closed position and all pressure relief will occur through thepressure release means 81. However, when the supply pressure isalternated betweeen the ports 44 and 46, then the leakage fluid withingear box chamber 62 will be alternately discharged through the pressurerelease means 81 or 92, depending upon which pressure release means isconnected to the discharge or low pressure port.

The latter-mentioned mode of operation is essential in situations wherethe hydraulic device 11 is used for driving vehicles where instantreversing of the hydraulic motor is necessary. This instant reversing ofthe hydraulic motor is accomplished by reversing the supply of pressurefluid from one of the openings 42 and 43 to the other of the openings 42and 43, which reversal causes the hydraulic cylinder barrel 26 and pumpshaft 21 to be rotated in the opposite direction. This reversal alsotends to cause excessive, short duration pressure build-ups to occurwithin the hydraulic motor. These short duration pressure build-ups orpressure pulses are instantaneously released, according to the presentinvention, due to the provision of the pressure release means 81 and 92,which pressure release means are connected to both of the port openings42 and 43 so that discharge to the low pressure port is possible at alltimes, even during such instantaneous reversals of rotatron.

However, in some use situations both port openings 42 and 43 of thehydraulic motor are subjected to a relatively high pressure. This canoccur when the high pressure supply fluid is supplied to one of theopenings 42 and 43, and the-other opening 42 and 43 is restricted, asfor braking the motor. In this situation, since the pressure within bothof the port openings 42 and 43 is relatively high, niether pressurerelease means 81 nor 92 can be opened to permit venting of the leakagefluid within the gear box chamber 62. Accordingly, to permit thehydraulic drive device 11 of the present invention to be utilized inthis type of use situation, the front cover 63 of the gear box isprovided with one or more discharge ports 93 formed therein, whichdischarge ports can be suitabley connected to the low pressure side ofthe fluid system, such as a fluid reservoir. However, in situationswhere hydraulic braking is not utilized, and where the pressure releasemeans 81 and 92 are sufficient to relieve the pressure within thechamber 62 due to instant shifting of the supply pressure between theopenings 42 and 43, then the discharge ports 93 are closed, as by use ofconventional threaded plugs 94. The auxiliary discharge ports 93 must beutilized only in use situations where high pressure may exist for anysubstantial period of time on both of the port openings 42 and 43.

Although a particular preferred embodiment of the invention has beendisclosed in detail for illustrative purposes, it will be recognizedthat variations or modifications of the disclosed apparatus, includingthe rearrangement of parts, lie within the scope of the presentinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

I. A hydraulic drive device, comprising in combination:

housing means defining therein a motor chamber; shaft means disposedwithin said motor chamber and rotatably supported on said housing means;

hydraulic motor means disposed within said motor chamber andinterconnected to said shaft means for rotating same, said motor meansincluding relatively sliding seal means disposed between high and lowpressure zones for substantially preventing pressure fluid from flowinginto the low pressure zone;

first and second port means formed in said housing means for enablingpressure fluid to be supplied to or discharged from said motor means;passage means providing communication between said low pressure zone andthe discharge one of said first and second port means for permittingflow therebetween of pressure fluid which leaks from said motor means,said passage means including first and second passageways communicatingwith said first and second port means, respectively; and

normally-closed pressure release means disposed with said passage meansfor preventing excessive pressure build-up of the leaded pressure fluidcontained within said low pressure zone, said pressure release meansincluding first and second check valves disposed within said first andsecond passageways, respectively, and oriented to be normally heldclosed by pressure in the port means.

2. In a hydraulic device having housing means defining a chambertherein, shaft means rotatably supported on said housing means andextending into said chamber, a cylinder block disposed within saidchamber and provided with a plurality of cylinder bores formed axiallytherein, said cylinder block being nonrotatably connected to said shaftmeans and having a cylinder port for each cylinder bore opening throughone axial end thereof, an inclined plate mounted on said housing meansand disposed adjacent the other axial end of said cylinder block, apiston slideably disposed within each of said cylinder bores andpositioned for engagement with said inclined plate, and said housingmeans includ ing a port plate disposed adjacent and in slideablyengagement with said one end of said cylinder block, said port platehaving two port openings formed therein and positioned to alternatelycommunicate with the cylin' der ports upon rotation of the cylinderblock,

the improvement comprising pressure release means disposed incommunication with said chamber for enabling external discharge of thepressure fluid which leaks past said pistons or past said axial end ofsaid cylinder barrel and collects within said chamber;

said pressure release means including passage means providingcommunication between said chamber and one of said port openigns, andone-waycheck valve means associated with said passage means forpermitting flow therethrough only when the pressure in said chamberexceeds the pressure in said one port opening; and

said passage means including an elongated bleed passage formed in saidcylinder block and extending between the opposite axial ends thereof.

3. A device according to claim 2 wherein said pressure release meansincludes further passage means providing communication between saidchamber and said other port opening and further one-way check valvemeans associated with said further passage means for permitting flowtherethrough only when the pressure in said chamber exceeds the pressurein said other port opening.

4. A hydraulic drive device, comprising in combination:

housing means defining therein a motor chamber and a gear box chamber;

a shaft disposed within said motor chamber and rotatably supported onsaid housing means, said shaft extending into said gear box chamber;

hydraulic motor means disposed within said motor chamber andinterconnected to said shaft for rotating same, said motor meansincluding a cylinder barrel nonrotatably connected to said shaft andhaving a plurality of cylinder bores formed therein and a pistonslideably disposed within each of said bores, said cylinder barrel alsohaving cylinder ports formed therein and communicating with each of saidcylinder bores for enabling pressure fluid to be supplied to ordischarged from said cylinder bores;

port meansformed in said housing means and communicating with saidcylinder ports for enabling pressure fluid to be supplied to ordischarged from said cylinder bores, said port means including two portopenings formed in said housing means and positioned for communicationwith the cylinder ports formed in said cylinder barrel, said two portopenings functioning as inlet and outlet ports for enabling pressurefluid to be supplied to and discharged from said cylinder bores;

output means rotatably supported on said housing means and extendinginto said gear box chamber;

reduction gear means disposed within said gear box chamber and drivinglyinterconnecting said shaft and said output means, said reduction gearmeans including a drive gear nonrotatably connected to said shaft and adriven gear nonrotatably connected to said output means;

passage means providing free communication between said motor chamberand said gear box chamher for permitting flow therebetween of pressurefluid which leaks from said motor means; and

pressure release means for preventing excessive pressure build-up of theleaked pressure fluid contained within said chambers, said pressurerelease means including a flow passage providing communication betweensaid gear box chamber and one of said port openings, and a one-way checkvalve disposed within said flow passage for permitting flow of fluidtherethrough whenever the pressure of the fluid within the gear boxchamber exceeds the pressure of the fluid within said one port opening.

5. A device according to claim 4, wherein said pressure release meansincludes a further flow passage providing communication between saidgear box chamber and the other port opening, and a further one-way checkvalve disposed in said further passage for permitting flow therethroughwhenever the pressure of the fluid within the gear box chamber exceedsthe pressure of the fluid in said other port opening.

6. A device according to claim 4, wherein said passage means includes ableed passage formed in said cylinder barrel and extending substantiallyaxially thereof, one end of said bleed passage communicating with saidgear box chamber and the other end of said bleed passage communicatingwith said motor chamber for enabling leakage fluid within said motorchamber to freely flow into said gear box chamber.

7. A device according to claim 4, wherein said drive gear comprises anexternally toothed gear member and said driven gear comprises aninternally toothed gear member disposed in meshing engagement with saiddrive gear, said driven gear having a diameter substantially larger thanthe diameter of said drive gear, and said output means including anoutput shaft nonrotatably connected to said driven gear and disposed forrotation about an axis substantially parallel to but laterally spacedfrom the rotational axis of said shaft means.

8. A device according to claim 4, wherein said cylinder bores extendaxially of said cylinder barrel in substantiqlly parallel relationshipto said shaft means, said motor means including an inclined platemounted on said housing means and axially spaced from one axial end ofsaid cylinder barrel for engagement by said pistons, and said gearreduction means being disposed adjacent the other axial end of saidcylinder barrel.

9. A device according to claim 8, wherein said housing means includes afixed porting member having a surface thereon in sliding engagement withsaid other axial end of said cylinder barrel, said other axial end ofsaid cylinder barrel having said cylinder ports formed therein, and saidtwo port openings being formed in said porting member and communicatingwith said surface of said porting member whereby said port openingsintermittently communicate with said cylinder ports.

10. A device according to claim 9, wherein said pressure release meansincludes a second one-way check valve means providing communicationbetween said gear box chamber and the other said port opening, each saidcheck valve means permitting free flow therethrough whenever thepressure in said gear box chamber is greater than the pressure in therespective port opening.

11. A device according to claim 10, wherein said cylinder barrel has ableed passage extending axially between the opposite ends thereof withone end of said bleed passage terminating at said one axial end of saidcylinder barrel and being in communication with said motor chamber, andthe other axial end of said bleed passage terminating adjacent saidother axial end of said cylinder barrel and being disposed incommunication with said passage means.

12. A device according to claim 10, wherein said passage means forproviding communication between said motor chamber and said gear boxchamber includes an annular clearance passage disposed between saidshaft means and said housing means, and antifriction bearing meansdisposed in said clearance space for rotatably supporting said shaft onsaid housing means, said bearing means having clearance spaces thereinfor enabling free flow of pressure fluid therethrough, and said cylinderbarrel having a bleed passage extending substantially axiallytherethrough with opposite axial ends of said bleed passagecommunicating with said annular clearance space and said motor chamber.

1. A hydraulic drive device, comprising in combination: housing meansdefining therein a motor chamber; shaft means disposed within said motorchamber and rotatably supported on said housing means; hydraulic motormeans disposed within said motor chamber and interconnected to saidshaft means for rotating same, said motor means including relativelysliding seal means disposed between high and low pressure zones forsubstantially preventing pressure fluid from flowing into the lowpressure zone; first and second port means formed in said housing meansfor enabling pressure fluid to be supplied to or discharged from saidmotor means; passage means providing communication between said lowpressure zone and the discharge one of said first and second port meansfor permitting flow therebetween of pressure fluid which leaks from saidmotor means, said passage means including first and second passagewayscommunicating with said first and second port means, respectively; andnormally-closed pressure release means disposed with said passage meansfor preventing excessive pressure build-up of the leaded pressure fluidcontained within said low pressure zone, said pressure release meansincluding first and second check valves disposed within said first andsecond passageways, respectively, and oriented to be normallY heldclosed by pressure in the port means.
 2. In a hydraulic device havinghousing means defining a chamber therein, shaft means rotatablysupported on said housing means and extending into said chamber, acylinder block disposed within said chamber and provided with aplurality of cylinder bores formed axially therein, said cylinder blockbeing nonrotatably connected to said shaft means and having a cylinderport for each cylinder bore opening through one axial end thereof, aninclined plate mounted on said housing means and disposed adjacent theother axial end of said cylinder block, a piston slideably disposedwithin each of said cylinder bores and positioned for engagement withsaid inclined plate, and said housing means including a port platedisposed adjacent and in slideable engagement with said one end of saidcylinder block, said port plate having two port openings formed thereinand positioned to alternately communicate with the cylinder ports uponrotation of the cylinder block, the improvement comprising pressurerelease means disposed in communication with said chamber for enablingexternal discharge of the pressure fluid which leaks past said pistonsor past said axial end of said cylinder barrel and collects within saidchamber; said pressure release means including passage means providingcommunication between said chamber and one of said port openigns, andone-way check valve means associated with said passage means forpermitting flow therethrough only when the pressure in said chamberexceeds the pressure in said one port opening; and said passage meansincluding an elongated bleed passage formed in said cylinder block andextending between the opposite axial ends thereof.
 3. A device accordingto claim 2 wherein said pressure release means includes further passagemeans providing communication between said chamber and said other portopening and further one-way check valve means associated with saidfurther passage means for permitting flow therethrough only when thepressure in said chamber exceeds the pressure in said other portopening.
 4. A hydraulic drive device, comprising in combination: housingmeans defining therein a motor chamber and a gear box chamber; a shaftdisposed within said motor chamber and rotatably supported on saidhousing means, said shaft extending into said gear box chamber;hydraulic motor means disposed within said motor chamber andinterconnected to said shaft for rotating same, said motor meansincluding a cylinder barrel nonrotatably connected to said shaft andhaving a plurality of cylinder bores formed therein and a pistonslideably disposed within each of said bores, said cylinder barrel alsohaving cylinder ports formed therein and communicating with each of saidcylinder bores for enabling pressure fluid to be supplied to ordischarged from said cylinder bores; port means formed in said housingmeans and communicating with said cylinder ports for enabling pressurefluid to be supplied to or discharged from said cylinder bores, saidport means including two port openings formed in said housing means andpositioned for communication with the cylinder ports formed in saidcylinder barrel, said two port openings functioning as inlet and outletports for enabling pressure fluid to be supplied to and discharged fromsaid cylinder bores; output means rotatably supported on said housingmeans and extending into said gear box chamber; reduction gear meansdisposed within said gear box chamber and drivingly interconnecting saidshaft and said output means, said reduction gear means including a drivegear nonrotatably connected to said shaft and a driven gear nonrotatablyconnected to said output means; passage means providing freecommunication between said motor chamber and said gear box chamber forpermitting flow therebetween of pressure fluid which leaks from saidmotor means; and pressure release means for preventing excessivepressure build-up of the leaked Pressure fluid contained within saidchambers, said pressure release means including a flow passage providingcommunication between said gear box chamber and one of said portopenings, and a one-way check valve disposed within said flow passagefor permitting flow of fluid therethrough whenever the pressure of thefluid within the gear box chamber exceeds the pressure of the fluidwithin said one port opening.
 5. A device according to claim 4, whereinsaid pressure release means includes a further flow passage providingcommunication between said gear box chamber and the other port opening,and a further one-way check valve disposed in said further passage forpermitting flow therethrough whenever the pressure of the fluid withinthe gear box chamber exceeds the pressure of the fluid in said otherport opening.
 6. A device according to claim 4, wherein said passagemeans includes a bleed passage formed in said cylinder barrel andextending substantially axially thereof, one end of said bleed passagecommunicating with said gear box chamber and the other end of said bleedpassage communicating with said motor chamber for enabling leakage fluidwithin said motor chamber to freely flow into said gear box chamber. 7.A device according to claim 4, wherein said drive gear comprises anexternally toothed gear member and said driven gear comprises aninternally toothed gear member disposed in meshing engagement with saiddrive gear, said driven gear having a diameter substantially larger thanthe diameter of said drive gear, and said output means including anoutput shaft nonrotatably connected to said driven gear and disposed forrotation about an axis substantially parallel to but laterally spacedfrom the rotational axis of said shaft means.
 8. A device according toclaim 4, wherein said cylinder bores extend axially of said cylinderbarrel in substantiqlly parallel relationship to said shaft means, saidmotor means including an inclined plate mounted on said housing meansand axially spaced from one axial end of said cylinder barrel forengagement by said pistons, and said gear reduction means being disposedadjacent the other axial end of said cylinder barrel.
 9. A deviceaccording to claim 8, wherein said housing means includes a fixedporting member having a surface thereon in sliding engagement with saidother axial end of said cylinder barrel, said other axial end of saidcylinder barrel having said cylinder ports formed therein, and said twoport openings being formed in said porting member and communicating withsaid surface of said porting member whereby said port openingsintermittently communicate with said cylinder ports.
 10. A deviceaccording to claim 9, wherein said pressure release means includes asecond one-way check valve means providing communication between saidgear box chamber and the other said port opening, each said check valvemeans permitting free flow therethrough whenever the pressure in saidgear box chamber is greater than the pressure in the respective portopening.
 11. A device according to claim 10, wherein said cylinderbarrel has a bleed passage extending axially between the opposite endsthereof with one end of said bleed passage terminating at said one axialend of said cylinder barrel and being in communication with said motorchamber, and the other axial end of said bleed passage terminatingadjacent said other axial end of said cylinder barrel and being disposedin communication with said passage means.
 12. A device according toclaim 10, wherein said passage means for providing communication betweensaid motor chamber and said gear box chamber includes an annularclearance passage disposed between said shaft means and said housingmeans, and antifriction bearing means disposed in said clearance spacefor rotatably supporting said shaft on said housing means, said bearingmeans having clearance spaces therein for enabling free flow of pressurefluid therethrough, and said cylinder barrel having a bleed passAgeextending substantially axially therethrough with opposite axial ends ofsaid bleed passage communicating with said annular clearance space andsaid motor chamber.